I think it’s a combination of “Poles got his guy”, he didn’t want to potentially lose out on Bates to other interested teams, and he also thinks Bates can be an above average center on a cheap contract, rather than overspending to bring in a legitimate starting center. We will have to wait to find out if Poles was correct in his assessment.
I don’t really think he was duped by the Bills. The facts were out there — Bates started for the Bills two seasons ago but he was on the bench last season. So either Poles sees something in Bates that the Bills didn’t, or Poles is wrong and Bates is just a backup quality OL.
A fifth rounder is not a massive loss. Many fifth round picks end up being cut anyways. Now Poles’ trade of the first pick in the second round for a lazy bum WR will forever be his legacy if he fails to get the job done with the Bears.